Hemolytic-uremic syndrome (HUS) is the most common cause of renal failure in children. HUS is a severe inflammatory disease, caused by Shiga toxin-producing E. coli, and is marked by the expression of proinflammatory mediators within the kidneys. Shiga toxin is a member of a large family of ribotoxins whose toxicity to cells stems from the depurination of a single adenine within the "sarcin/ricin" loop of 28S ribosomal RNA (28S rRNA). The depurination of 28S rRNA results not only in the inhibition of protein translation, but also the intense and extended activation of the stress-activated protein kinases such as JNK and p38 MAPK. These kinases are central mediators of inflammatory responses that are responsible for inducing the transcription of proinflammatory cytokines and chemokines. An insufficient understanding of the primary target tissues of Shiga toxins and the mechanisms that drive the proinflammatory and cytotoxic responses has impeded the development of interventional remedies for HUS. The administration of Shiga toxins to experimental animals such as rats and mice has failed to recapitulate the renal hallmarks of HUS that involve glomerular pathologies. We have developed a mouse model of HUS that is induced by administration of ricin, a ribotoxin that has an identical ribosomal target as Shiga toxins, but that binds to receptors present on all cells. We will employ ricin in mice and primary cultured cells (macrophages and cells derived from glomeruli) to elucidate the initial targets of action, the cytotoxic consequences, and the cellular and molecular mechanisms that lead to HUS. I. We will determine the activation of gene expression induced by ricin and LPS in glomeruli in experimental HUS, in wild-type mice and in mice that are deficient in TNF and IL-I receptors: II. We will determine the genes that are activated, and the signaling pathways involved, in cultured cells of the renal glomerulus. III. We will characterize the apoptotic mechanisms in experimental HUS by elucidating the involvement of apical caspase 8 and by determining whether caspase inhibitors can ameliorate the cytotoxic consequences of ricin administration. [unreadable] [unreadable] [unreadable]